Pressure control for lapping device

ABSTRACT

A plurality of pivotally mounted members are arranged in a plane parallel to and spaced from a lapping surface and relative to the path of movement of an element so as to move the element axially and to provide a pressure pattern comprising a number of incrementally increasing and/or decreasing pressures with which the element can be maintained in engagement with the lapping surface. Each of the pivotal members is responsive to the force exerted thereagainst by a gas- or liquid-actuated plunger. With a group of such members arranged relative to the path of travel of the element, the pressure with which the element is maintained against the lapping surface can be varied to increase uniformly from one end to the other, to decrease uniformly from one end to the other, or to provide a number of variable pressures throughout the path of travel during the lapping operation. In other words, a pressure pattern can be devised for any one or a combination of material, lapping speed, element hardness, etc.

United States Patent Bender 1541 PRESSURE CONTROL FOR LAPPING DEVICE[72] Inventor: David L. Bender, West Henrietta,

[73] Assignee: Hamco Machine 8: Electronics Corp., Rochester, N.Y.

[22] Filed: Sept. 21,1970

[21] Appl. No.: 73,978

-[52] US. Cl ..51/134, 51/1659 [51] Int. Cl. ..B24b 7/04 [58] Field ofSearch ..5l/l34, 165.9; 125/11 TP [56] References Cited UNITED STATESPATENTS 3,492,762 2/1970 Heinrich ..5 1/1 34 2,282,038 5/1942 Davenport..l25/11 TP 3,369,328 2/1968 Freerks ..5l/l65.9

FOREIGN PATENTS 0R APPLICATIONS 171,620 11/1921 Great Britain ..51/134[451 Se t. 19, 1972 Primary Examiner-Harold D. Whitehead Attorney-LloydF. Seebach [57] ABSTRACT A plurality of pivotally mounted members arearranged in a plane parallel to and spaced from a lapping surface andrelative to the path of movement of an element so as to move the elementaxially and to provide a pressure pattern comprising a number ofincrementally increasing and/or decreasing pressures with which theelement can be maintained in engagement with the lapping surface. Eachof the pivotal members is responsive to the force exerted thereagainstby a gasor liquid-actuated plunger. With a group of such membersarranged relative to the path of travel of the element, the pressurewith which the element is maintained against the lapping surface can bevaried to increase uniformly from one end to the other, to decreaseuniformly from one end to the other, or to provide a number of variablepressures throughout the path of travel during the lapping operation. Inother words, a pressure pattern can be devised for any one or acombination of material, lapping speed, element hardness, etc.

3 Claims, 3 Drawing Figures PATENTEDSEP 1 9 19 2 3.691; 69?

sum 1 or 3 Wu MW DAV/D L. BENDER INVENTOR. 1 M

AGENT PATENTEDSEP 19 I972 sum 2 or 3 DAV/D L. BE/VDER INVENTOR. w mixAGENT PRESSURE CONTROL FOR LAPPING DEVICE FIELD OF THE INVENTION Theinvention relates to a lapping device and more particularly to anarrangement for controlling the pressure and for providing a pressurepattern with which the surface of an element that is to be lapped ismaintained against the surface of a lapping wheel.

DESCRIPTION OF THE PRIOR ART It is well known in the lapping art toprovide apparatus that is capable of imparting a smooth surface to aplanar surface or to a peripheral surface of an element. It is customaryto mount a number of elements, particularly if in the form of a glassdisc or a lens, on a carrier by means of pitch or other suitableadhesive materials. The carrier is usually rotated with respect to apolishing or lapping member that is also rotated, or rotated andoscillated. However, when lapping a material such as glass, a chip froma disc or a lens that is being lapped can be carried under the polishingmember and cause damage to the other discs or lenses that are mounted onthe same carrier.

When lapping thin crystal wafers of a material, such as germanium,silicon or a similar material, that are used in the field of electronicsas the basic element for a transistor, the general principles forlapping or polishing glass are usually followed for polishing the planarsurfaces of the crystal material to a thickness and para]- lelism ofvery small tolerance. The number of wafers that might be scratched ormade unusable due to cracking or chipping during the lapping operationcan result in a relatively high cost having to be applied to thosewafers that are successfully lapped without damage. One of the primarycauses for cracking or chipping wafers during the lapping operation isthe pressure with which the wafer is maintained against the surface ofthe lapping wheel.

In US. Pat. No. 3,492,762, issued on Feb. 3, 1970 to Robert G. Heinrich,a lapping device is disclosed in which individual crystal wafers orelements are maintained in engagement with a lapping surface by means ofan arcuate, planar cam which moves each discrete holder of a crystaltoward the lapping surface as it is moved into proximity thereto andholds the wafer in engagement with the lapping surface throughout itsmovement in that portion of its designated path which intersects thelapping surface. It has been found that best results can be obtained,not only as to smoothness of the surface being lapped but also withrespect to damage to the wafer, when the pressure with which the waferis maintained against the lapping surface can be varied to provide apattern of pressure throughout the portion of its path through which itis moved during the lapping operation, such a pressure pattern takinginto account the type of material, the lapping speed, the requiredsmoothness tolerance, etc.

SUMMARY OF THE INVENTION The primary object of the invention is toprovide a suitable control for maintaining a surface of an element to belapped in engagement with a lapping surface with a preset or designatedpressure pattern throughout its movement along a path and relative tothe lapping surface.

Another object of the invention is to provide a suitable control wherebyan element can be maintained against a lapping surface with anincrementally variable pressure throughout its path of travel.

Still another object of the invention is to provide a control comprisinga plurality of independently adjustable pressure members for maintainingan element against a lapping surface with a preset or designatedpressure pattern throughout its path of travel relative to the lappingsurface.

The above objects and advantages of the invention are attained bypositioning an element to be lapped on a supporting member mounted on arotatable carrier that moves each element across and relative to aplanar lapping surface. The element is retained on a holder that can berotated as well as moved axially toward and away from the lappingsurface independent of the rotation of the carrier. A plurality ofpivotally mounted members are arranged in a plane parallel to and spacedfrom the lapping surface and relative to the path of movement of theelement so as to move the element axially and to provide a pressurepattern comprising a number of incrementally increasing and/ordecreasing pressures with which the element can be maintained inengagement with the lapping surface. Each of the pivotal members isresponsive to the force exerted thereagainst by a gasor liquid-actuatedplunger. With a group of such members arranged relative to the path oftravel of the element, the pressure with which the element is maintainedagainst the lapping surface can be varied to increase uniformly from oneend to the other, to decrease uniformly from one end to the other, or toprovide a number of variable pressures throughout the path of travelduring the lapping operation. In other words, a pressure pattern can bedevised for any one or a combination of material, lapping speed, elementhardness, etc.

With such a pressure control arrangement, the movement of theelement tobe lapped toward the lapping surface is accomplished and maintained byeach respective pivotal member. The means by which each element isreturned to a position in which it is displaced from the lapping surfaceis accomplished by air pressure or resilient means associated with eachrespective supporting member on the carrier. Inasmuch as the workingpressures can be adjusted in increments throughout the path of travel,various materials can be easily accommodated to the same lapping surfaceor the lapping characteristics of the surface and which might bedependent on the lapping pressure.

Other objects and advantages of the invention will be apparent to thoseskilled in the art by the description which follows.

DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanyingdrawings wherein like reference numerals designate like parts andwherein:

FIG. 1 is a front elevational view of a lapping device embodying theinvention;

FIG. 2 is a plan view showing particularly the drive means for movingthe lapping wheel and the carrier as well as the drive means for eachindividual element holder; and

FIG. 3 is a vertical sectional view through a supporting member showingone of several pressure control members by which the element ismaintained in engagement with the lapping surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION With referenceparticularly to FIGS. 1 and 2, a support means comprises a bedplate 11which is mounted on a suitable framework (not shown) so that thebedplate is positioned at a workable height for an operator. A lappingmember 12 including its associated spindle or shaft is rotatably mountedin a bracket 13 that is fixed to a support bracket 14 which, in turn, ismounted on the bedplate.

The lapping member 12 comprises a cast disc 15 having a lapping wheel 16secured thereto in any well known manner. The lapping member 12 overliesa carrier 20 on which a plurality of supporting members designated bythe numeral 21 are rotatably mounted. The carrier 20 is rotated by meansof a motor 22 that is connected by a belt 23 to a pulley 24 on a shaft25 to which the carrier is fixed. The carrier 20 moves the supportingelements 21 in an arcuate path across a portion of the lapping wheel 16as seen in FIG. 2. The lapping member 12 is rotated by a motor 26 bymeans of a belt 27 which engages a pulley 28 on the associated spindleor shaft 29 of member 12 that is rotatably mounted in bracket 13, asseen in FIGS. 1 and 2 and as shown and described in the above-mentionedUS. Pat. No. 3,492,762.

The drive means for rotating the supporting members 21 comprises a motor30which drives a pulley 31 connected by a belt 32 to a pulley 33 (lower)on a shaft 34; the latter also carrying another pulley 35 (upper)arranged above pulley 33. A plurality of pulleys 36 are arranged aroundthe periphery of carrier 20, in a pattern as shown in FIG. 2, and areconnected by a belt 37 to the one pulley 35 that is on the same shaft aspulley 33. The pulley, 36 are arranged in the same plane as a pulley 72(see FIG. 3) on each of the supporting members 21 which will bedescribed in more detail hereinafter. It will be noted from FIG. 2 thatthe belt 37 engages only those pulleys 36 on the supporting members 21that are immediately near and directly under the lapping member 12. Bythis arrangement, the drive means for supporting members 21 is coupledonly to those supporting members moved into positions immediately aheadof, aligned with and immediately beyond the lapping member 12.

From the description thus far, it is evident that the lapping member 12is continuously rotated and the car rier 20 is rotated to move thesupporting members 21 in a circular path, a portion of which intersectsthe surface of the lapping member 12. Also, as the supporting members 21are moved in this path, rotation of those members leaving andapproaching the lapping member 12 is started and ended with engagementand disengagement with belt 37. As pointed out in the above patent, thepurpose for rotating the supporting members 21 while in engagement withthe lapping member 12 is to produce a smoother surface finish with onlysingle pass under the lapping member 12.

As shown in FIG. 2, the carrier 20 supports a plurality of supportingmembers 21, all of which are identical and the following description is,therefore, applicable to each of the members 21. A mounting member 40,see FIG. 3, comprises a flange portion 41 which rests on the uppersurface 42 of the carrier 20 and a sleeve portion 43 which extendsthrough an opening 44 in member 20 and toward bedplate 11. The flange 41is fixed to carrier 20 by suitable fastening means, such as bolts whichare not shown, so as to hold the member 40 in a fixed relation tocarrier 20. A pair of bearings, each of which is designated by numeral45, is mounted in member 20 and with respect to an inner sleeve 46. Theupper bearing 45 is retained in position by a lock ring 47 and the lowerbearing 45 is retained by a threaded ring 48.The inner sleeve 46 servesas a bearing for a tubular member 50, which rotates with sleeve 46 as aunit but is held against rotation relative to sleeve 46 by the set screw51 but which can be moved axially for a purpose to be describedhereinafter and limited in its axial movement by the slot 52 which isengaged by the end of set screw 51. The tubular member 50 is providedwith a flange 53 at its upper end which supports a cup-shaped shield 54.

The shield 54 is retained or clamped in position by a holder 55 whichoverlies shield 54 and is fixed or secured to flange 53 by suitablescrews, not shown. The external face 56 of holder 55 supports areplaceable collar 57 which is provided with a circular recess 58 and isretained in position by set screws 59 which engage the peripheral groove60 in the holder 55. A wafer supporting member 61 is fixed to surface 62of collar 57 and is provided with a circular recess 63 which isinterconnected to surface 64 thereof by a plurality of holes 65 and apatterned recess of grooves or enlarged holes 66 and to recess 58 by ahole or holes 67. The external thread 68 is threadably engaged by aplastic retained ring 69 which prevents any sidewise motion of wafer orelement 70 positioned thereon and retained by a suitable vacuum.

The retained ring 68 is, preferably, removed from each of the supportingmembers 61 in order to establish a common plane of the same height foreach of surfaces 64. This is attained by moving the supporting members21 successively into contact with the lapping member 12 to establishsuch plane. Once the common plane or height has been established forsurfaces 64, a ring 69 is returned to each of respective members 61.

The inner sleeve 46 carries a pulley 72 which is fixed to the sleeve atits lower end by a key 73. The tubular member 50 also carries at itslower end a follower 74 having an insert 75 which is joined by aconnector 76 to a source for producing a vacuum or a source ofpressurized air. The vacuum is used to retain the elements 70 on theirrespective member 61 during movement from a loading station, through theabrading station and to an unloading station. In the latter station, airis applied to remove the element. The vacuum or air is directed fromconnector 76 through a central bore 71,

an axial direction toward surface 16 of the lapping member 12.

The pulley 72 is engaged by the belt 37 as the supporting member 21 withits respective holder 55 and element 70 approaches the lapping member12. Before the supporting member 21 is actually moved under the lappingsurface 16, the inner sleeve 46 and member 50 start to rotate uponengagement of belt 37 by pulley 72, such rotation being imparted totubular member 50 and the element 70 carried or supported therebythrough the set screw 51 and slot 52. At this point, the tubular member50 is at its lowest point with respect to the inner sleeve 46 and theinsert 75 is merely spaced from the facing surface of bedplate 11 withsufficient clearance for normal movement in its path.

In the portion of the arcuate path through which the supporting members21 are moved when under the lapping member 12, there is arranged aplurality of members that are in spaced relation to the carrier andprovide means for moving the supporting member with its respectiveelement toward the abrading or lapping surface 16 and for maintainingthe surface of the element 70 to be lapped in engagement with thelapping surface. Such means is shown in FIG. 3 and is only one ofseveral arranged in this portion of the path. Specifically, the pressurecontrol means comprises a plate 80 that is pivotally mounted at 81 in ablock 82 fixed to the surface 83 of bedplate 11. At the end of plate 80opposite its pivot, a shoulder screw 84 is arranged to provide a maximumlimit of movement for the plate 80. Beneath each of plates 80, acylinder 90 is mounted with respect to plate 11 and is provided with aplunger 91 which extends through plate 1 1 and engages the under side ofplate 80 as shown in FIG. 3. Each of cylinders 90 is connected by a line92 to a source (not shown) of either a gas or a liquid medium forvarying the pressure exerted by plunger 91 on plate 80.

As shown in FIG. 1, a plurality of plates 80 are arranged on bedplate l1and each of the plates is connected through a suitable control valve 94to the source of either a gas or a liquid medium. Also, each ofcylinders 90 is associated with a meter or gauge 95 which indicates thepressure being applied to its respective cylinder.

Depending on the type of material that is to be lapped, the pressureapplied to each respective cylinder can be the same to provide aconstant pressure as the element 70 is moved through the portion of itspath with respect to the lapping member 12, can be varied such that thepressure will increase from the entry side of the path to the exit side,or can be varied as an independent increment by each .respectivecylinder 90. In this way, complete control of the pressure with whichthe element 70 is urged against the lapping surface 16 can be obtainedand a predetermined pressure pattern can be established in accordancewith the material, the lapping speed, the required tolerances, etc.,- asdescribed above.

As shown in the drawings and described above, the pivotally mountedplates 80 are arranged on the bedplate 11 in an arcuate pattern whichcorresponds to the portion of the path of movement of the elements underthe lapping surface 16. As the carrier 20 moves a supporting member 21toward the lapping member 12, the insert 75 engages a ramp surface 85 onthe leading plate 80 and is moved upward and with such movement thetubular member 50 and the element 70 are moved therewith. Thepressurewith which the element will be maintained against the lappingsurface 16 will be dependent on the preset pressure with respect to eachof the cylinders 90. The force exerted on the plate 80 by the plunger 91minus the combined weights of plate 80 and member 50 with its associatedparts will determine the pressure with which the element 70 ismaintained against the surface 16. The maximum axial travel of thetubular member 50 and element 70 toward the lapping surface 16 isdetermined by the preset position of the nut 78 along the threaded end77 of the tubular member.

As each of the supporting members 21 is moved relative to the lappingsurface 16, the pressure exerted on the tubular member 50 can be variedin increments, the number of increments being dependent on the number ofplates 80 forming the path through which the element 70 is moved.Inasmuch as each of plates 80 can be individually adjusted to provide adifferent pressure, the pattern of pressures across the group of plates80 can assume any pattern that is desirable for the particular materialthat is being lapped. It should be readily apparent to one skilled inthe art that such a pressure pat tern that lends itself to being readilyadjusted for various types of materials is one which also will permit amaximum surface smoothness to be obtained with a particular type ofcutting surface; for example, a very fine or very coarse abradingsurface.

As described in the above-mentioned patents, the element 70 is retainedon the member 61 by means of a vacuum which is connected to the tubularmember 50 via connector 76. When the supporting member 21 reaches thepoint in its path where it is no longer under the lapping wheel 16, theinsert rides off of the last plate via a ramp and moves toward thesurface 83 of bedplate 21 by gravity. In this lower position, the setscrew 51 will then abut the upper end of the slot 52.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

I claim:

1. In a device for abrading a surface of an element retained on a holderthat is arranged relative to the abrading surface of a rotatable memberand movable axially toward and away from said abrading surface and in apath at least a portion of which intersects said abrading surface; theimprovement comprising:

a plurality of independently adjustable members forming a track arrangedin generally spaced, parallel relation to said portion of said path forengagement by said holder;

each member being pivotally mounted along an edge thereof andoperatively engaging means for establishing an independent operatingpressure with which the surface of said element is maintained againstsaid abrading surface as said holder is moved thereover; and

each of said members moving said holder axially toward said abradingsurface and maintaining the surface of said element against saidabrading sur face with a pressure independent of that of each of theother members.

2. The abrading device in accordance with claim 1 wherein said pressuremeans comprises a pneumatically operable plunger in engagement with saidmember adjacent the other edge thereof.

3. The abrading device in accordance with claim 1 5 including meansoperatively connected to each of said pressure means for establishing anindependent operating pressure.

1. In a device for abrading a surface of an element retained on a holder that is arranged relative to the abrading surface of a rotatable member and movable axially toward and away from said abrading surface and in a path at least a portion of which intersects said abrading surface; the improvement comprising: a plurality of independently adjustable members forming a track arranged in generally spaced, parallel relation to said portion of said path for engagement by said holder; each member being pivotally mounted along an edge thereof and operatively engaging means for establishing an independent operating pressure with which the surface of said element is maintained against said abrading surface as said holder is moved thereover; and each of said members moving said holder axially toward said abrading surface and maintaining the surface of said element against said abrading surface with a pressure independent of that of each of the other members.
 2. The abrading device in accordance with claim 1 wherein said pressure means comprises a pneumatically operable plunger in engagement with said member adjacent the other edge thereof.
 3. The abrading device in accordance with claim 1 including means operatively connected to each of said pressure means for establishing an independent operating pressure. 